This invention relates to an electric flash discharge device for use in, for example, a camera.
Conventionally, as a light source for a camera is used a flash discharge tube which is caused to emit light by the discharge current of the capacitor connected thereto. Since the amount of light emitted from the discharge tube can be controlled by controlling the discharge current of the capacitor, an automatic light-emission control, which is made in such a manner as the tube receives light reflected from a foreground subject to be photographed and automatically stops emitting light in accordance with the amount of the light thus received, can be employed with the discharge tube. Generally, however, the service life of the discharge tube is shortened as the discharge current rapidly increases. In a conventional flash discharge device, therefore, an inductance element is connected in series with the device, thereby to make the rise in the discharge current slower so as to suppress the maximum value of the discharge current to not so large a value. However, where as in the case of an endoscope camera used to take a photograph of the interior of, for example, a human body, a large amount of light is required, the amount of the current as large as several hundreds of amperes occasionally flows, at the time of the peak, in the discharge tube. In order to make the series resistance of the inductance sufficiently small, therefore, the coil winding of the inductance element must be made of a very thick wire. This means that the flash discharge tube device becomes large in size and weight and therefore becomes inconvenient to use as a light source for the camera. Further, since an electric current flows in the coil, an electromagnetic flux is developed therein to have undesirable effects upon the other associated parts or to cause generation of sounds due to the electromagnetic force, thus to make a patient examined by the endoscope more uneasy than adequately expected or estimated. Further, since the inductance value is made unlikely to vary, there exists almost no room to freely vary the waveform of the discharge current. Not a few inconveniences, therefore, occur in respect of control of the amount of light from the discharge tube and maintenance of it.
There has also been proposed a flash discharge tube, as described in Japanese patent application disclosure No. 3622/74, in which a constant current circuit is connected to a discharge circuit of the tube to control the discharge tube to keep it at a specified value. In such type of discharge tube, however, it is indeed possible to control the amount of light from the tube. But, since upon commencement of the discharge the amount of the discharge current rapidly increases to the above-mentioned value, the problem that the service life of the tube shortens cannot be solved.